Several scientific or patent publications are referenced in this patent application to describe the state of the art to which the invention pertains. Each of these publications is incorporated by reference herein, in its entirety.
Mammals respond to tissue injury, trauma or infection by executing a complex series of biological reactions in an effort to prevent further tissue damage, to initiate repair of damaged tissue, and to isolate and destroy infective organisms. This process is referred to as the inflammatory response, the early and intermediate stages of which are referred to as the acute phase response.
The acute phase response involves a wide variety of mediators, including cytokines, interleukins and tumor necrosis factor. It also involves a radical alteration in the biosynthetic profile of the liver. Under normal circumstances, the liver synthesizes a range of plasma proteins at steady state concentrations. Some of these proteins, the “acute phase” proteins are induced in the inflammatory response to a level many times greater than levels found under normal conditions. Acute phase proteins are reviewed by Steel & Whitehead (Immunology Today 15: 81–87, 1994).
One of the massively induced acute phase proteins is Serum Amyloid A (SAA). SAA actually comprises a family of polymorphic proteins encoded by many genes in a number of mammalian species. SAAs are small apolipoproteins that accumulate and associate rapidly with high-density lipoprotein 3 (HDL3) during the acute phase of the inflammatory response. Most SAA isoforms are induced in response to inflammation; however, certain SAAs (e.g., human SAA4) appear to be constitutively expressed or minimally induced in the inflammatory response.
The liver has been considered the primary site of SAA production. However, SAA production outside the liver has been found, on a limited basis. For instance, expression of SAA mRNA has been reported in human atherosclerotic lesions and in human cultured smooth muscle cells and monocyte/macrophage cell lines (Meek et al., 1994; Urieli-Shoval et al., 1994; Yamada et al., 1996), and a unique isoform of SAA (SAA3) is produced by rabbit synovial fibroblasts (Mitchell et al., J. Clin. Invest. 87: 1177–1185, 1991). More recently, it was discovered that SAA mRNA is widely expressed in many histologically normal epithelial tissues, including tissues of stomach, intestine, tonsil, breast, prostate, thyroid, lung, pancreas, kidney, skin and brain neurons (Urieli-Shoval et al., J. Histochem. Cytochem. 46: 1377–1384, 1998). The role of SAA in such tissues has not been elucidated, nor has it been determined if the SAAs present in those tissues are the same isoforms as those found in serum, or if they represent additional isoforms of SAA.